Light olefins, defined herein as ethylene, propylene, butylene and mixtures thereof, serve as feeds for the production of numerous important chemicals and polymers. Typically, light olefins are produced by cracking petroleum feeds. Because of the limited supply of competitive petroleum feeds, the opportunities to produce low cost light olefins from petroleum feeds are limited. Efforts to develop light olefin production technologies based on alternative feeds have increased.
Important alternate feeds for the production of light olefins are oxygenates, such as, for example, alcohols, particularly methanol and ethanol, dimethyl ether, methyl ethyl ether, diethyl ether, dimethyl carbonate, and methyl formate. Many of these oxygenates may be produced by fermentation, or from synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials, including coal, recycled plastics, municipal wastes, or any organic material. Because of the wide variety of sources, alcohol, alcohol derivatives, and other oxygenates have promise as an economical, non-petroleum source for light olefin production.
The catalysts used to promote the conversion of oxygenates to olefins are molecular sieve catalysts. Because ethylene and propylene are the most sought after products of such a reaction, research has focused on what catalysts are most selective to ethylene and/or propylene, and on methods for increasing the life and selectivity of the catalysts to ethylene and/or propylene.
The process for converting a feedstock, especially a feedstock containing one or more oxygenates, in the presence of a molecular sieve catalyst composition according to the invention, is carried out in a reaction process in a reactor, where the process is a fixed bed process, a fluidized bed process, preferably a continuous fluidized bed process, and most preferably a continuous high velocity fluidized bed process.
The reaction processes can take place in a variety of catalytic reactors such as hybrid reactors that have a dense bed or fixed bed zones and/or fast fluidized bed reaction zones coupled together, circulating fluidized bed reactors, riser reactors, and the like. Suitable conventional reactor types are described in, for example, U.S. Pat. No. 4,076,796, U.S. Pat. No. 6,287,522 (dual riser), and Fluidization Engineering, D. Kunii and O. Levenspiel, Robert E. Krieger Publishing Company, New York, N.Y. 1977, which are all herein fully incorporated by reference.
The preferred reactor types are riser reactors generally described in Riser Reactor, Fluidization and Fluid-Particle Systems, pages 48 to 59, F. A. Zenz and D. F. Othmer, Reinhold Publishing Corporation, New York, 1960, and U.S. Pat. No. 6,166,282 (fast-fluidized bed reactor), and U.S. patent application Ser. No. 09/564,613 filed May 4, 2000 (multiple riser reactor), which are all herein fully incorporated by reference.
In a preferred embodiment of oxygenates to olefins conversion, a fluidized bed process or high velocity fluidized bed process is employed which includes a reactor system, a regeneration system and a recovery system.
In order to optimize operation of oxygenates conversion to light olefins, it is desirable to control various parameters associated with the oxygenate to olefins conversion reactor. Such control can enhance oxygenate conversion and/or selectivity for prime olefins, especially for ethylene and propylene.
U.S. Pat. No. 6,166,282 to Miller teaches a process for converting oxygenates to light olefins in a fast-fluidized bed reactor and further observes that oxygenate conversion processes can be sensitive to reaction variables such as temperature, catalytic activity, and space velocity.
U.S. Pat. No. 5,952,538 to Vaughn et al. discloses an optimal range of space velocities which are suitable for oxygenates to olefin conversion.
Gayubo, et al, Ind. Eng. Chem. Res. 2000, 39, 292–300, disclose that in conversion to olefins, higher average reaction temperatures at a given coke level on the catalyst increases selectivity to ethylene.
U.S. Pat. No. 6,137,022 to Kuechler et al. discloses oxygenates to olefins conversion in the presence of silicoaluminophosphate molecular sieve-containing catalyst which maintains an optimal feedstock conversion between 80% and 99% under conditions effective to convert 100% of the feedstock when the reaction zone contains at least 33 volume percent of the silicoaluminophosphate molecular sieve.
U.S. Pat. No. 6,023,005 discloses the importance of maintaining optimal average coke levels on oxygenates to olefins conversion catalyst to effect improved lower olefin selectivity.
Infrared (IR) analysis of various process streams for the purpose of process control is known in the prior art.
U.S. Pat. No. 6,103,934 to Hallinan et al. discloses a process control method for producing acetic acid by catalyzed carbonylation of methanol in which various reactor component concentrations, e.g., active catalyst, methyl iodide, water and methyl acetate are measured using an infrared analyzer. The concentrations are adjusted in response to the measurements taken to optimize the acetic acid reaction.
U.S. Pat. No. 6,228,650 to Moore et al. discloses controlling concentration of alkylation catalyst components HF acid, acid soluble oil (ASO) and water, by measuring a continuously flowing catalyst slip stream in an IR analyzer and using the results to vary temperature of stripping fluid in order to control ASO levels within a preferred range.
U.S. Pat. No. 6,162,644 to Choi et al. teaches controlling separation and isomerization of xylene isomer by analyzing various streams provided by the process using near IR (NIR). The analysis results are utilized for on-line monitoring, process control and process optimization for producing para-xylene.
U.S. Pat. No. 5,862,060 to Murray, Jr. discloses controlling chemical processes using compositional data, as the basis for control using NIR spectroscopy which allows for on-line measurements in real time. A calibration set of NIR spectra bounding the acceptable process space for a particular controlled property is assembled and a multivariant statistical method is applied to the calibration step to identify a small number (2–4) of the characteristics of the set governing the controlled property. Thus a complex process can be controlled in such a way as to provide a substantially invariant product composition.
Deru Qoin et al., “Quantitative Analysis of Process Streams by Online FTIR Spectrometry,” Anal. Chem (1997), 69(10), 1942–1945, teaches an online method for real-time characterization of gas streams containing trimethylamine and methanol using Fourier Transform Infrared (FT-IR) spectrometry with multivariate methods, e.g., partial least squares, to obtain quantitative information for process control.
U.S. Pat. No. 5,470,482 to Holt teaches controlling para-xylene purity or recovery in a moving bed para-xylene separation process. The process measures concentrations of para-xylene, meta-xylene, ortho-xylene, and ethylbenzene in various streams by NIR or mid-range FT-IR and operating variables adjusted in response.
U.S. Pat. No. 5,407,830 discloses control of catalyst composition in an HF alkylation unit by sampling and analyzing feedstreams using infrared spectroscopy to generate signals which are compared to reference signals in order to generate difference signals which control the flow of individual reactor feed components.
All of the foregoing references are incorporated by reference herein in their entirety.
Variations over time in oxygenate to olefins reactor effluent composition can cause difficulties in subsequent effluent processing required to obtain products which meet the requirements for desired end uses. Effluent stream fluctuations in composition can overload separations used to obtain polymer grade olefin streams, resulting in products which are outside the desired specification, e.g., containing unacceptably high levels of oxygenate, or highly unsaturated olefins such as diolefins and acetylenes. The present invention provides a simple and effective method for controlling oxygenates to olefins reactor systems so that a consistent reactor effluent stream can be obtained. While the extent of oxygenates conversion can be determined from many types of effluent stream analyses, it is difficult to obtain such an analysis fast enough for the results to be useful for oxygenates to olefins reactor control. Accordingly, it would be desirable to provide a process for controlling an oxygenates to olefin reactor which provides a substantially consistent effluent stream, by sampling the product stream to determine the extent of oxygenate conversion. In particular, it would be desirable to sample and analyze effluent samples within a time frame sufficient to provide effluent analysis results that can be used to control reactor conditions, in order to maintain a substantially consistent effluent.